Method and apparatus for forming composite material and composite material therefrom

ABSTRACT

A system and method for extruding composite material and the composite material therefrom. The composite material consists of a filler mixed with a binding agent. The composite material is extruded as billets with enhanced physical properties, such as color, texture, electrical conductivity and fire retardancy, and contains a dispersion pattern of the filler material. A system and method are also provided for drawing the composite material through a die and a composite material produced thereby. The drawn composite material exhibits a density reduction over the density of the starting material and enhanced physical properties. A particularly useful tongue and groove arrangement are also provided for joining adjacent strips of a composite material made according to the extrusion process.

This application claims the benefit of provisional application Ser. No.60/172,586, filed Dec. 20, 1999.

The present application claims priority from PCT/CA00/01555 filed Dec.19, 2000.

FIELD OF THE INVENTION

The present invention relates to extrusion processes. In particular, thepresent invention relates to an extrusion method and apparatus forcomposite material.

BACKGROUND OF THE INVENTION

The process of solid-state extrusion is known. Extrusion processes thatare used include ram extrusion and hydrostatic extrusion. Ram extrusionutilises a chamber in which polymer billets are placed, one end of whichcontains a die and the other an axially mobile ram. The billet is placedwithin the chamber such that the sides of the billet are touching thesides of the chamber. The mobile ram pushes the billets and forces themthrough the die.

In hydrostatic extrusion processes, the billet is of a smaller size thanthe chamber and does not come into contact with the sides of thechamber. The chamber contains a pressure generating device at one endand a die at the other. The space between the billet and the chamber isfilled with a hydraulic fluid, pumped into the chamber at the endcontaining the pressure generating device. During operation pressure isincreased on the hydraulic fluid and this in turn transmits pressure tothe surface of the billet. As the billet passes through the die some ofthe hydraulic fluid adheres to the surface of the billet, providingadditional lubrication to the process.

Both processes produce a polymer that is oriented in a longitudinaldirection, having increased mechanical properties, such as tensilestrength and stiffness. However, the orientation in a longitudinaldirection can also make the polymer weak and subject to transversecracking or fibrillation under abrasion. The process of pushing thepolymer through a die can also create surface imperfections caused byfrictional forces.

U.S. Pat. No. 5,204,045 to Courval et al. discloses a process forextruding polymer shapes with smooth, unbroken surfaces. The processincludes heating the polymer shape to below the melting point of thepolymer and then extruding the polymer through a die that is heated to atemperature at least as high as the temperature of the polymer. Theprocess also involves melting a thin surface layer of the polymer toform a thin, smooth surface layer. The process produces a material of auniform appearance and subsequent commercial applications are limited asa result.

SUMMARY OF THE INVENTION

A composite material comprising an oriented polymer and a particulatefiller dispersed throughout the oriented polymer. The composite materialhas a reduced density which is less than the combined masses of theoriented polymer and a particulate filler divided by their combinedrespective volumes.

The oriented polymer maybe of plastic and the particulate filler may beselected from the group consisting of wood, slate, talc, vermiculite andmica.

The plastic may be polypropylene, polyethylene and polyvinyl chlorideand present in an amount of from 95% to 60% by weight a compared to theparticulate filler.

According to one embodiment, the oriented polymer is polypropylene andthe particulate filler is wood sawdust having a particle size of about60 mesh and present in amount of from 20% to 30% by weight as comparedto the weight of the oriented polymer.

A process for producing an oriented composite material, said processcomprising the steps of combining:

-   -   (i) an extrudable polymer with a particulate filler to form a        starting material;    -   (ii) heating and extruding said starting material into a first        column;    -   (iii) adjusting the temperature of said first column to a        drawing temperature;    -   (iv) presenting said first column to a drawing die and causing        said first column to exit said drawing die in a second column        having a cross-sectional area less than that of said first        column;    -   (v) applying a pulling force to said second column to draw said        first column through said drawing die at a rate sufficient to        cause orientation of said polymer and to cause said second        column diminish in density to form said composite material.

The extrudable polymer may be of plastic, such as polypropylene,polyethylene or polyvinyl chloride.

The particulate filler may be wood, slate, talc, vermiculite or mica.

The extruable polymer may be present in an amount of from 95% to 60% byweight in the starting material.

According to one embodiment, the extruable polymer is polypropylene, theparticulate filler is wood sawdust having a particle size of about 60mesh, the wood sawdust being present in an amount from about 20% to 30%by weight in the starting material.

The rate of drawing through the drawing die may be sufficient to causethe composite material to have a density of from 0.5 to 0.9 of thedensity of the starting material.

A composite material is provided which includes a filler for enhancingthe physical properties of the composite material and a binding agentmixed with the filler for permitting extrusion of the composite materialin a plastic extrusion process to provide a predetermined dispersingpattern of the filler in the composite material.

The filler may be natural or synthetic fiber and the binding agent maybe a polymer.

A composite material is provided which comprises a particulate materialdispensed in an oriented polymer.

The particulate material may be wood sawdust having a particle size ofabout 60 mesh. The oriented polymer may be polyethylene with theoriented polymer forming from 60% to 95% by weight of the compositematerial.

A strip of composite material is provided, suitable for strip flooringand having parallel upper and lower faces with first and second paralleledges extending between the upper and lower faces. The first edge has atongue extending therefrom with parallel upper and lower curvedsurfaces. The second edge has a groove extending thereinto with curvedparallel opposite sides. The tongue and the groove are of complimentarycurvature for the tongue of a first strip to be rotatable intoregistration with the groove of an adjacent strip to resist lateralseparation between the first strip, and the adjacent strips byinterference between the upper and lower curved surfaces and the curvedparallel opposite sides.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the attached Figures, wherein:

FIG. 1 illustrates a method of extruding a composite material accordingto the present invention;

FIG. 2 illustrates an extruder for extruding same;

FIG. 3 illustrates an extruded billet of the composite material;

FIG. 4 is an end elevation of a tongue and groove joint which may beformed in the extrusion method of the present invention;

FIG. 5 is a cross-sectional illustration of an alternate forming methodaccording to the present invention; and

FIG. 6 is a schematic illustration of an automated process of the methodof FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 a method of extruding a composite material isshown generally at 10. A filler 12 and a binding agent 14 are placed ina feeder 16. Feeder 16 feeds a predetermined volume of filler 12 andbinding agent 14 into melt extruder 18. In an embodiment, feeder 16 is agravimetric feeder controlled by an external CPU 17. Melt extruder 18mixes filler 12 and binding agent 14 to form feedstock 20, as is wellknown to those of skill in the art. Feedstock 20 then passes to anextruder 22, and is extruded to produce a composite material 24.

Filler 12 can be a natural fibre, such as wood and agricultural fibressuch as hemp, flax, straw or wheat; a synthetic fibre such as nylon,polyethylene terephthalate, glass or polypropylene fibre with apolyethylene matrix. Filler 12 can also be a mineral based filler suchas slate, talc, vermiculite or mica. In a presently preferredembodiment, filler 12 is a wood fibre concentrate. Filler 12 has a meshin the range of 10-300, more preferably in the range 10-150. In thepresently preferred embodiment filler 12 has a 60 mesh.

Binding agent 14 is a polymer or other suitable extrudable plastic, suchas polypropylene (PP), polyethylene (PE) or polyvinyl chloride (PVC).Binding agent 14 forms approximately 55-95% by weight of feedstock 20.Other ranges for the % weight of binding agent 14 in feedstock 20 may beappropriate depending on the filler chosen. More limited ranges of60-95% or 70-90% may be required depending on the chosen filler 12.

Once filler 12 and binding agent 14 have been fed to feeder 16, theypass to melt extruder 18. A predetermined volume of filler 12, inaccordance with the % weight of binding agent 14 that is used, andbinding agent 14 are mixed in melt extruder 18 and extruded in aconventional manner to produce feedstock 20. The resultant feedstock 20is fed by melt extruder 18 to extruder 22.

FIG. 2 illustrates a preferred embodiment of extruder 22. Extruder 22has a ram 34, a pressure chamber 30 and a die 38. The method andapparatus of the extrusion process are detailed in U.S. Pat. No.5,169,589 to Francoeur et al., U.S. Pat. No. 5,204,045 to Courval et al.and U.S. Pat. No. 5,169,587 to Courval, the contents of which areincorporated herein by reference. The method of the extrusion processproduces a highly oriented polymer profile. The resultant compositematerial 24, produced by this process, generally has a higher tensilestrength and modulus than feedstock 20. In the presently preferredembodiment an oriented product 48 of composite material 24, formed witha wood-fibre concentrate filler is produced in standard widths of 2inches, 3 inches or 6 inches (5.08 cm, 7.62 cm or 15.24 cm).

FIG. 3 illustrates an oriented product 48 of composite material 24.Produced in the manner outlined above, composite material 24 hasstriations 50 of filler 12, formed in a dispersion pattern with awood-grain appearance. The resultant oriented product 48 resembles hardwood flooring and can be adapted to be used in commercial applicationsas such. Appropriate attaching means, such as a tongue and groove, orsnap lock, can be subsequently tooled in to the oriented material tocreate a product that can be attached in series in a commercialapplication, such as flooring of furniture manufacturing. Surfacetreatment can also be applied to the billet for increasing the surfaceproperties of the billet, such as adding a protective coating, such aspolyurethane, to protect the surface layer from scratching.

By varying parameters of the ram extrusion process, such as temperature,pressure and die contours, properties of composite material 24 can bechanged. The properties of composite material 24 can also be changed byvarying amounts of filler 12, and by changing the composition of filler12. This will affect the physical properties of composite material 24,such as colour, texture, electrical conductivity, glow in the dark andfire retardancy.

The oriented product 48 of composite material 24 can be manipulated inorder to meet a manufacturer's specifications with regards to the finalcommercial application. Oriented product 48 can be cut and shaped duringthe ram extruding process. In the presently preferred embodiment,composite material 24 is extruded as oriented product 48 of varyingspecifications, however it can also be extruded as a sheet for use incommercial applications such as indoor and outdoor furnituremanufacturing.

The present invention provides a new composite material, and a methodand apparatus for extruding the composite material. The inventionincludes the initial mixing of a binding agent and a filler to produce afeedstock which is subsequently extruded as a billet of a compositematerial. The composite material is stronger and more durable then thestarting materials. The composite material also contains striations ofthe filler which allows the manufacturer to produce a composite materialthat can reflect the image of a natural product and can be used incommercial applications such as floor coverings. The properties of thecomposite material can also be changed, in order to meet therequirements for the commercial application of the product, by theincorporation of different types of filler and by varying the amount offiller used.

FIG. 4 is an end elevation showing a particularly advantageous tongueand groove configuration which can be formed along opposite edges of theoriented product 48 of the composite material 24. A first edge 50 has atongue 52 formed thereon having an upper concave face 54 and a lowerconvex face 56. The opposite edge 60 has a groove 62 with an upperconvex edge 64 and a lower concave edge 66. The tongue 52 and the groove62 register to allow the tongue to be initially inserted into the groove62 of an adjacent strip of oriented product 48 at a relative angle onthe order of 45° between the adjacent strips of oriented product 48 andthen rotated into place in the direction of arrow 70 so that the tongue52 nests in the groove 62 with the adjacent strips of oriented productin a parallel side by side configuration.

Once the tongue 52 and the groove 62 are nested, removal in a lateraldirection indicated by arrows 80 is prevented first by interferencebetween an upper edge 58 of the tongue and a depending edge 68 of thegroove. Lateral separation is further inhibited by an upwardly extendingedge 69 of the groove 62 interfering with a lowermost portion 59 of thetongue 52.

Extrusion rates for the composite material 24 will vary depending onvarious factors such as the particular composite material 24 selected,the degree of reduction, and the cross-sectional area of the extrudedstrip or column. Extrusion rates are however rather slow and rates onthe order of six inches per minute (6 in./min.) are not atypical.

It has been found that rater than extruding the composite material 24,by pressing it through the die 38, the composite material may be drawnthrough the die 38. FIG. 5 illustrates such a drawing process.

One manner of drawing the composite material through the die 38 is toinitially commence by extrusion, as discussed above. Once an end 100 ofthe oriented product 48 begins to emerge from the die 38, the end may begrasped, such as by a clamp 102 and pulled. The pulling would typicallybe done with no further pressing force being applied and yields anoriented end product 104.

In tests, pulling rates of up to 14 ft./min. (fourteen feet per minute)have been achieved which was limited by machine capacity. It is expectedthat pulling rates of 20 ft./min. (twenty feet per minute) are entirelyfeasible.

The properties of the oriented end product 104 produced by drawing aresignificantly different than those produced by extrusion. By way ofexample, a starting billet 110 was first formed by combining a woodfiber plastic concentrate containing 60% wood particles of about 60 meshsize and 50% polypropylene with virgin polypropylene in a 1:1 ratio.This yielded a composition having about 30% wood fiber and 70%polypropylene. The resulting combination was heated and extruded to formthe billet 110.

The billet 110 was of rectangular cross-section measuring about twoinches by two inches (2″×2″). The billet 110 was heated in an oven toabout 150° C. (ie. close to but below the melting point of polypropylenewhich is about 160° C.) and transferred to the pressure chamber 30 andinitially forced through the die 38. The extruded material was thengrasped using the clamp 102 and drawn at a rate of about 4 ft./min.(Four feet per minute) and once it had been entirely drawn through thedie 38, allowed to cool into the oriented end product 104. The drawratio (i.e. the initial cross-sectional area divided by the finalcross-sectional area) was 10:4.

The oriented end product 104 bore a remarkable similarity both in lookand in feel to wood. The oriented end product 104 diminished in densityby about half compared to the starting billet 110. The density of theoriented end product 104 was about 0.59 g/cc (grams per cubiccentimeter) compared to a density of about 1 g/cc for the startingbillet 110.

The oriented end product 104 could be shaped as if it were wood and inplaning and sawing behaved very much like wood producing shavingsremarkably like wood shavings and sawdust remarkably like wood sawdust.The oriented end product 104 received both nails and screws withoutsplitting much like wood.

In testing, the oriented end product was found to have a density andflexural strength not unlike wood and a modulus of elasticity of abouthalf that of wood. Typical properties were a density of 0.059 g/cc,flexural strength of 6,353 lb/in² and a modulus of elasticity of 799,298lb/in². Unlike wood however the oriented product 104 was virtually nonadsorptive to water.

Although testing was carried out using a starting billet 110, theprocess can no doubt be automated as schematically illustrated in FIG.6. FIG. 6 shows an extruder 120 in which feed materials 121 may beblended and extruded through a die 122 into a first column 124. Thefirst column 124 is fed through a first haul off 125 into a continuousfurnace 126 where its temperature is adjusted to a drawing temperature.The first haul off 125 acts against the extrusion direction to maintainextrusion pressure and to support the column 124. The temperatureadjusted first column 124 is fed into a drawing die 128 at the exit ofwhich it is reduced in size to a second column 130. The second column130 is grasped by a suitable haul off 132 such as sold under thetrademark CATERPILLAR as it exits the drawing die 128. The haul off 132then pulls the second column 130 at a desired rate to form an orientedproduct 138.

The above-described embodiments of the invention are intended to beexamples of the present invention and alterations and modifications maybe effected thereto, by those of skill in the art, without departingfrom the scope of the invention which is defined solely by the claimsappended hereto.

1. A process for producing an oriented composite material, said processcomprising the steps of: i) combining an extrudable polymer with acellulose based particulate filler to form a starting material; ii)heating and extruding said starting material into a first column; iii)adjusting the temperature of said first column to a drawing temperature;iv) presenting said first column to a drawing die and causing said firstcolumn to exit said drawing die in a second column having across-sectional area less than that of said first column; v) applying apulling force to said second column to draw said first column throughsaid drawing die at a rate sufficient to cause orientation of saidpolymer and to cause said second column to diminish in density to formsaid composite material.
 2. A process according to claim 1 wherein: saidextrudable polymer is selected from the group consisting ofpolypropylene, polyethylene and polyvinyl chloride.
 3. A processaccording to claim 1 wherein: said extrudable polymer is a plastic; andsaid particulate filler is selected from the group consisting of wood,hemp, flax, straw and wheat.
 4. A process according to claim 2 wherein:said extrudable polymer is present in an amount of from 95 to 60 percentby weight in said starting material.
 5. A process according to claim 4wherein: said particulate filler is selected from the group consistingof wood, hemp, flax, straw and wheat.
 6. A process according to claim 5wherein: said extrudable polymer is polypropylene; and said particulatefiller is wood sawdust.
 7. A process according to claim 5 wherein: saidwood sawdust has a particle size of about 60 mesh.
 8. A processaccording to claim 7 wherein: said wood sawdust in present in an amountof from about 20% to 30% by weight in said starting material.
 9. Aprocess according to claim 1 wherein; said second drawing die has adrawn ratio of from 4 to
 20. 10. A process according to claim 1 wherein;said rate of drawing through said drawing die is sufficient to causesaid composite material to have a density of from 0.5 to 0.9 of thedensity of said starting material.